1. Field of the Invention
The invention relates and pertains to tapping attachments, particularly those of the self-reversing variety, and to coolant systems for use in connection with such tapping attachments, tapping attachment being tools connectable to a source of rotational power for the purpose of imparting rotational drive to a tap held in such tapping attachment, whereby a threaded hole is made.
2. Description of the Prior Art
The field of the invention is represented by prior art patents including U.S. Pat. Nos. 3,397,588; 3,472,347; 3,717,892; 3,946,844; 3,999,642; 4,014,421; 4,029,429, 4,067,424 and 5,011,344. All are assigned to the assignee of this application.
Tapping attachments, and in particular self-reversing tapping attachments, comprise a crowded and highly developed art. Tapping attachments are tools connectable to a source of rotational drive and for holding a tap used to make threaded holes. Self-reversing tapping attachments are those which contain means for reversing the direction of rotation of the tap so as to facilitate withdrawal thereof from a threaded hole.
Increased demands recently placed upon tapping attachments have resulted in new constraints and requirements upon tapping equipment. In particular, the advent of Computer Numeric Control (CNC) of tapping operations has fostered a requirement of rapid and precise operation of tapping attachments and of the taps carried by them. Accompanying the development of high speed, high performance tapping, under CNC or manual control, is a need for providing coolant to tapping attachments and in particular to the tap and the workpiece in which the taps make a threaded holes. Such coolant provides not only cooling but also clears debris such as cuttings and the like from the workpiece. Co-pending patent application Ser. No. 07/330,752 filed Mar. 30, 1989, now abandoned, assigned to the assignee of the instant application, discloses and claims a coolant conduit arrangement which is suitable for regular tapping applications. Other existing devices also make provision for furnishing a coolant to a tap and the workpiece.
Existing devices such as the tapping attachment described in co-pending application Ser. No. 07/330,752 filed Mar. 30, 1989 to the same assignee and related Continuation-in-Part application Ser. No. 07/715,343, filed Jun. 14, 1991 provide coolant conduits to achieve the purposes referred to above. Under extremely high speed and/or high-pressure conditions, however, and under conditions where the tap may have a smaller coolant opening and cross-section than the coolant conduit in the tapping attachment, problems can arise due to back pressure of the coolant flow.
When there is back pressure in tapping attachments which are self-reversing such as those described in the above-specified co-pending applications and in other existing devices, such back pressure not only can result in a loss of coolant to the tap and an escape of fluid into parts of the system where it should not be, but also such back pressure can directly adversely affect the operation of the spindle and tap themselves. This is due to the fact that in self-reversing tapping attachments, the tap is subjected to reverse rotation for the purpose of facilitating its withdrawal from the threaded hole. Under this arrangement, existing devices provide for relative axial movement of the spindle driver along the direction of the drive spindle for the purpose of shifting into reverse drive. Thus, back pressure can cause unwanted motion or forces tending to cause such motion relative to the spindle and its driver, to the detriment of the tapping operation itself.
Therefore, there has been a felt but unfulfilled need for a self-reversing tapping attachment having a coolant system whereby problems associated with back pressure of coolant can be resolved.